1. Field of the Invention
The present invention relates to methods of making improved ammoxidation catalysts for the production of unsaturated nitriles from their corresponding olefins.
2. Description of Related Art
Several publications are referenced in this application. The references describe the state of the art to which this invention pertains and are hereby incorporated by reference.
It is known in the art that the bismuth-molybdenum system plays a role in electron donor/acceptor mechanisms for selective oxidation and ammoxidation. Therefore different mechanisms have been proposed based on this property [Delmon et al. (New Development in Selective Oxidation by Heterogeneous Catalysis, Vol. 72, 1992, p. 399-413) and Encyclopedia of Chemical Technology (Kirk-Othmer, Vol. 1, 4th edition, page 358)]. In these mechanisms, molybdenum was shown to be responsible for oxygen and nitrogen uptake and insertion into the substrate, while bismuth plays the role of H-abstraction of the methyl group in the xcex2 position. Therefore, bismuth and molybdenum should be present on the catalyst surface and adjacent in order to form the suitable active phase for this reaction. It should be noted that the deficiency of bismuth on the catalyst surface leads to the total oxidation reaction of the substrate.
It is also well known that antimony plays the role of a donor and thus could improve the selectivity of the catalyst. Antimony can also play an additional role of isolating the vanadium active centers which are highly active towards the oxidation reaction. This leads to minimizing the total oxidation reaction and directs the reaction towards the desired product.
Many catalysts have been disclosed for the foregoing reactions. One such catalyst is described in U.S. Pat. No. 4,062,885, where BiMoSbV systems were used as active elements. The catalyst was used for the preparation of phthalonitrile by the ammoxidation of ortho-xylene. The use of such catalysts for oxidation or ammoxidation reactions involving unsaturated aliphatic hydrocarbons is not mentioned.
U.S. Pat. No. 4,040,978 relates to a catalyst for ammoxidation reactions containing bismuth molybdate mixed with other elements.
U.S. Pat. No. 4,405,498 relates to a catalyst for oxidation and ammoxidation reactions containing BiMoVSb with additional elements selected from groups IA, IIA, IVA, VA, VIA, IB, IVB and VIIB of the periodic Table of the Elements. Elements from group VB of the periodic table are not disclosed in this patent.
U.S. Pat. No. 4,600,541 relates to a catalyst comprising FeBiMo and promoters such as Pd, Pt, Os and Ir.
More recently, European Patent Publication No. 0 475 351 A1 relates to a catalyst containing KFeSbMo which could be promoted by Nb and W. The best yield was achieved with a catalyst of the formula Fe10Sb10Mo9Bi2K0.6Ni5.5W0.3B0.75P0.75 (SiO2)70.
European Patent Publication No. 0 573 713 B1 relates to a catalyst comprising MoBiFeCoNiCr promoted with at least three other promoters selected from alkali metals, alkaline earth metals, rare earth metals, Nb, Tl and As, with Fe, Co, Ni and Cr as essential catalyst components.
U.S. Pat. No. 5,688,739 relates to a multi-component catalyst. The base of this catalyst is bismuth molybdenum. Germanium was added as an essential element. The use of niobium was not disclosed in this patent.
None of the prior art references discloses or suggests catalysts which provide high performance for the selective production of unsaturated nitrites from their corresponding olefins. Accordingly, it would be desirable to produce an improved catalyst for use in the selective production of unsaturated nitrites from their corresponding olefins.
It is an object of the invention to overcome the above-identified deficiencies.
It is another object of the invention to provide a useful, improved catalyst for the production of nitrites from their corresponding olefins, particularly for the production of acrylonitrile from propylene.
It is a further object of the invention to provide a process for making an improved catalyst for the production of acrylonitrile at high yields by vapor phase catalytic ammoxidation of propylene in a fluidized or fixed bed reactor.
The foregoing and other objects and advantages of the invention will be set forth in or apparent from the following description.
The present invention relates to an improved catalyst for the production of unsaturated nitrites from their corresponding olefins and methods of making and using the same. More specifically, the invention relates to improved methods of making such catalysts and the resultant improved catalysts.
Preferably, the catalyst has the following empirical formula set forth below:
BiaMObVcSbdNbeAfBgOx, wherein
A=one or more elements selected from groups VB (e.g. V, Nb, Ta), VIB (e.g. Cr, Mo, W), VIIB (e.g. Mn, Tc, Re) or VIII (e.g. Fe, Co, Ni) of the periodic table;
B=at least one alkali promoter selected from groups IA (e.g., Li, Na, K) or IIA (e.g., Mg, Ca) of the periodic table;
a=0.01 to 12;
b=0.01 to 12;
c=0.01 to 2;
d=0.01 to10;
e=0.01 to 1;
f=0 to 2, preferably from 0.01 to 1;
g=0 to 1, preferably from 0.001 to 0.5; and
x=the number of oxygen atoms required to satisfy the valency requirements of the elements present.
The numerical values of a, b, c, d, e, f, g, and x represent the relative gram-atom ratios of the elements, respectively, in the catalyst, where x is a number required to satisfy the valence requirements of the other elements. The elements are present in combination with oxygen, preferably in the form of various oxides.
The invention also relates to an improved selective low temperature catalytic process for the production of nitrites from their corresponding olefins, particularly for the production of acrylonitrile from propylene.
Other objects as well as aspects, features and advantages of the present invention will become apparent from a study of the present specification, including the claims and specific examples.
One aspect of the invention relates to methods for preparing catalysts for the production of unsaturated nitrites.
One embodiment of the invention relates to a method for preparing a catalyst for olefin ammoxidation, said catalyst containing bismuth, molybdenum, vanadium, antimony, and niobium, comprising the steps of:
(a) preparing a vanadium antimonate phase by heating a slurry of vanadium oxide and antimony oxide thereby forming a vanadium-antimony paste and subsequently drying the paste and calcining to form said vanadium antimonate phase;
(b) preparing a niobium-molybdenum solution;
(c) preparing bismuth, niobium, and molybdenum mixed oxide hydrates at room temperature and without heat treating said mixed oxide hydrates;
(d) combining said vanadium antimonate phase, said mixed oxide hydrates and a support thereby forming a catalyst precursor mixture;
(e) stirring the catalyst precursor mixture for a period of time sufficient to form a catalyst precursor paste; and
(f) drying said catalyst precursor paste to form a dried catalyst precursor material and calcining said dried catalyst precursor material to form said catalyst.
Preferably, the catalyst has the following empirical formula:
BiaMobVcSbdNbeAfBgOx, wherein:
A=one or more elements selected from the group consisting of groups VB, VIB, VIIB, and VIII of the periodic table;
B=at least one alkali promoter selected from the group consisting of groups IA and IIA of the periodic table;
a=0.01 to 12;
b=0.01 to 12;
c=0.01 to 2;
d=0.01 to 10;
e=0.01to 1;
f=0 to 2, preferably from 0.01 to 1;
g=0 to 1, preferably from 0.001 to 0.5; and
x=the number of oxygen atoms required to satisfy the valency requirements of the elements present.
Preferably, the vanadium oxide is V2O5 and/or the antimony oxide is Sb2O3.
Preferably, the calcining in step (a) is at a temperature ranging from 600 to 950xc2x0 C., more preferably 700 to 850xc2x0 C., even more preferably from 740 to 780xc2x0 C. and most preferred about 750xc2x0 C.
Preferably the calcining in step (a) is in the presence of air and/or oxygen.
Preferably, the niobium-molybdenum solution is prepared at a pH of 3.0 to 10, more preferably a pH of 3.5 to 9, even more preferably a pH of 3.5 to 5.
According to one preferred embodiment, step (c) comprises adding bismuth to said niobium-molybdenum solution and precipitating said mixed oxide hydrates at room temperature and without heat treating of said mixed oxide hydrates.
Preferably, step (c) comprises rash co-precipitation of bismuth, niobium, and molybdenum mixed oxide hydrates. More preferably, step (c) comprises adding a solution containing bismuth to said niobium-molybdenum solution.
According to one preferred embodiment, the support comprises pre-acidified silica. Preferably, step (d) comprising incorporating said vanadium antimonate phase and said mixed oxide hydrates in pre-acidified silica colloidal.
According to another preferred embodiment, the method further comprises boiling said catalyst precursor mixture to form said catalyst precursor paste.
Preferably, the stirring in step (e) is vigorous stirring, as opposed to gentle or mild stirring.
According to one preferred embodiment, the catalyst precursor paste is dried at a temperature ranging from 80xc2x0 C. to 200xc2x0 C., preferably from 100xc2x0 C. to 150xc2x0 C., more preferably from 110xc2x0 C. to 130xc2x0 C. and most preferred about 120xc2x0 C.
According to another preferred embodiment, the calcining of said dried catalyst precursor material is at a temperature ranging from 450 to 650xc2x0 C., more preferably from 500 to 600xc2x0 C., even more preferably about 550xc2x0 C.
Preferably, the calcining of said dried catalyst precursor material is under an airflow or in the presence of air.
The catalysts of the invention can be used with or without a support. Preferably, the catalyst is a support ed catalyst. Suitable supports for the catalysts include alumina, silica, titania, zirconia, zeolites, silicon carbide, carbide, molecular sieves and other micro/nonporous materials, and mixtures thereof. When used on a support, the supported catalyst usually comprises from about 10 to 50% by weight of the catalyst composition, with the remainder being the support material.
Preferably, the support is selected from silica, alumina, zirconia, titania, alundum, silicon carbide, alumina-silica, inorganic phosphates, silicates, aluminates, borates and carbonates, pumice, montmorillonite, or mixtures thereof. More preferably, the support is silica. Preferably, the resultant catalyst comprises 40-70% by weight support.
According to another embodiment, the catalyst contains niobium derived from niobium pentoxide or niobium derived from a niobium source soluble in water. Preferably, the niobium-molybdenum solution is prepared using niobium derived from niobium pentoxide or using niobium derived from a niobium source soluble in water.
Preferably, step (a) comprises drying said paste at a temperature ranging from 80xc2x0 C. to 200xc2x0 C., more preferably from 100xc2x0 C. to 150xc2x0 C., even more preferably from 110xc2x0 C. to 130xc2x0 C. and most preferred about 120xc2x0 C.
Another embodiment of the invention relates to a method for preparing a catalyst for olefin ammoxidation, said catalyst containing bismuth, molybdenum, vanadium, antimony, and niobium, comprising the steps of;
(a) preparing a niobium-molybdenum solution at a pH of 3.5 to 10;
(b) adding bismuth to said niobium-molybdenum solution and precipitating bismuth, niobium, and molybdenum mixed oxide hydrates at room temperature and without heat post-treatment of said mixed oxide hydrates;
(c) combining a vanadium antimonate phase and said mixed oxide hydrates of bismuth, niobium, and molybdenum with pre-acidified silica colloidal thereby forming a catalyst precursor mixture;
(d) stirring the catalyst precursor mixture for a period of time sufficient to form a paste; and
(e) drying said paste to form a dried material and calcining said dried material to form said catalyst.
Yet another embodiment of the invention relates to a method for preparing a catalyst for olefin ammoxidation, said catalyst containing bismuth, molybdenum, vanadium, antimony, and niobium, comprising the steps of:
(a) preparing a vanadium antimonate phase;
(b) preparing a niobium-molybdenum solution at a pH of 3.5 to 10 ;
(c) adding bismuth to said niobium-molybdenum solution and precipitating bismuth, niobium, and molybdenum mixed oxide hydrates without heat post-treatment of said mixed oxide hydrates;
(d) combining said vanadium antimonate phase and said mixed oxide hydrates of bismuth, niobium, and molybdenum with pre-acidified silica colloidal thereby forming a catalyst precursor mixture;
(e) stirring the catalyst precursor mixture for a period of time sufficient to form a paste; and
(f) drying said paste to form a dried material and calcining said dried material to form said catalyst.
One particularly preferred embodiment of the invention relates to a method of making an improved ammoxidation catalytic system for the production of unsaturated nitrites from their corresponding olefins, in particular, for the production of acrylonitrile from propylene. More specifically, the present invention is directed to a method of making an improved ammoxidation catalyst containing niobium as an essential element for enhancing activity and selectivity of the catalyst system.
Another preferred embodiment of the invention relates to methods of making the catalysts described in copending U.S. application Ser. No. 09/228,885, filed Jan. 11, 1999, now U.S. Pat. No. 6,037,304, issued Mar. 14, 2000.
The Examples set forth below demonstrate the advantages achieved using the invention by showing the surprising effect of certain factors in preparing the catalyst.
Another aspect of the invention relates to methods of using the catalyst system of the invention. More specifically, the invention relates to an improved method of producing unsaturated nitrites from their corresponding olefms.
One preferred embodiment of the invention relates to an improved process for the catalytic preparation of acrylonitrile or metha acrylonitrile by the reaction of propylene or isobutylene with molecular oxygen and ammonia at a temperature of between about 200 to 600xc2x0 C. using the ammoxidation catalytic system of the invention.
Preferably, the process achieves a propylene conversion of at least 65%, more preferably at least 70% and most preferred at least 75% using the catalytic system of the invention.
Preferably, the selectivity in mol % to acrylonitrile is greater than 80%, more preferably greater than 85%. The yield of acrylonitrile in mol % is preferably greater than 50%, more preferably greater than 55%, even more preferably greater than 60% and most preferred greater than 65%.